1. Field of the Invention
The invention relates to a cetane number determination apparatus for a fuel of a diesel engine and a method of determining a cetane number of a fuel of a diesel engine.
2. Description of the Related Art
It is necessary in a diesel engine, as well as a gasoline engine, to handle various types of fuel in the optimal way. It is important, in terms of reducing emission and improving drivability, to detect a cetane number and perform the optimal fuel injection timing control.
The cetane number is a numerical index that indicates difficulty of diesel knocking occurrence in a diesel engine (that is, knocking resistance or an anti-knocking property), and that indicates self-ignitability. The cetane number is correlated with a delay of ignition. As the cetane number becomes larger, self-ignition is more likely to occur, and knocking is less likely to occur.
Various technologies for determining the cetane number have been proposed (for example, refer to Japanese Patent Application Publication No. 2004-340026 (JP-A-2004-340026)).
The cetane number hardly influences the combustion characteristics in a normal operation region, that is, when a normal fuel injection amount is used. Therefore, it is not easy to accurately determine the cetane number in the normal operation region.
Further, for example, as a method of determining the cetane number, it is conceivable to set a threshold of a heat generation rate dQ/dθ, thereby determining the ignition timing. However, this requires a complicated process, such as a differentiation process, and moreover, the determination result is likely to include a noise when this method is used.